Try in either /Library/PreferencePanes or ~/Library/PreferencePanes (where ~ is your Home directory. ie- /Users/your_username/).
I'm not on my machine at work that has ARD installed, but it is possible that it could be located in /System/Library/PreferencePanes, which would probably require either logging in as root or going to the Terminal application and typing
sudo rm -rf then a space
Then dragging the PreferencePane into the Terminal window. (Terminal.app will auto-complete the path to the PreferencePane for you).
If you have the ARD Admin app you should just be able to drag it to the Trash from /Applications. If not you'll have to use the Terminal trick described above.
Let us know what you find out. I will check back tomorrow when I'm at my work machine with ARD on it.
**Update** Apple Remote Desktop is installed in /System/Library/PreferencePanes. It is called ARDPref.prefpane